Skin conditions, such as herpes infections, are a widespread medical problem, with an increasing rate of prevalence. It has been reported that topically administered acyclovir, can be included in an effective protocol for the treatment of herpes infections. The topical application of acyclovir (2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]-6H-purin-6-one) has multiple purposes including the treatment or prevention of mucocutaneous infections such as oral labial (“fever blisters”), gingivostomatitis; and ophthalmically for keratoconjuntivitis and recurrent epithelia keratitis.
For optimal performance a topical acyclovir product should maximize the acyclovir concentration delivered to the layer of the skin where the virus resides. It is believed that in oral labial infection the virus resides in melanocytes at the epidermal-dermal junction. These cells lie 60-140 μm beneath the skin surface. In-vivo measurement in humans of acyclovir transport into the dermis has been performed using Zovirax® and microdialysis for monitoring delivered acyclovir (Br. J Dermatol. 2003 March; 148(3):434-43; The role of stratum corneum and dermal microvascular perfusion in penetration and tissue levels of water-soluble drugs investigated by microdialysis; Morgan C J, Renwick A G, Friedmann P S). The IC50 of Zovirax® cream (5%) against herpes simplex virus-1 isolates ranges from 0.02-13.5 mcg/mL and 0.01-9.9 mcg/mL for herpes simplex virus-2. (2006 Physicians Desk Reference entry for Zovirax cream.) In the study performed by Morgan et al., no acyclovir was detected in the dermis after application of acyclovir to intact skin. An acyclovir concentration of 3.9 μg/ml was achieved only after removal of the stratum corneum and reduction of cutaneous circulation by infusion of 0.0005% noradrenaline. (See Morgan, C J, ibid). Neither approach is suitable for a commercial product, but demonstrates the role of the stratum corneum as the main barrier to acyclovir transport, and the rapid clearance of acyclovir from the dermis due to cutaneous circulation.
There is a need for a composition which provides concentrations of acyclovir at the epidermal/dermal junction and would therefore increase its therapeutic benefits in the treatment of herpes simplex virus infection, including type 1 and type 2 herpes simplex viruses. Providing higher levels of acyclovir to the epidermal/dermal junction via topical administration may also increase indications for topical therapy.